Python: Count of elements in each group from list based groups of elements
Python List: Exercise - 216 with Solution
Write a Python program to group the elements of a list based on the given function and returns the count of elements in each group.
- Use collections.defaultdict to initialize a dictionary.
- Use map() to map the values of the given list using the given function./li>
- Iterate over the map and increase the element count each time it occurs.
Sample Solution:
Python Code:
from collections import defaultdict
def count_by(lst, fn = lambda x: x):
count = defaultdict(int)
for val in map(fn, lst):
count[val] += 1
return dict(count)
from math import floor
print(count_by([6.1, 4.2, 6.3], floor))
print(count_by(['one', 'two', 'three'], len))
Sample Output:
{6: 2, 4: 1} {3: 2, 5: 1}
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Previous: Write a Python program to merge two or more lists into a list of lists, combining elements from each of the input lists based on their positions.
Next: Write a Python program to split values into two groups, based on the result of the given filtering function.
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Python: Tips of the Day
Find current directory and file's directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
import os cwd = os.getcwd()
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
- os.path.dirname(path) (returns "the directory name of pathname path")
- os.getcwd() (returns "a string representing the current working directory")
- os.chdir(path) ("change the current working directory to path")
Ref: https://bit.ly/3fy0R6m
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